https://openjdk.java.net/ 
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
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package jdk.javadoc.internal;

import java.util.ResourceBundle;
import java.util.stream.Collectors;

import static java.util.ResourceBundle.getBundle;

public final class Versions {

    private Versions() { throw new AssertionError(); }

    
Returns the version of the javadoc tool and the Standard doclet. 
 This is typically the same as the version of the JDK platform being
used to run the tool, but may be different when running the tool on an
older version of the platform.

Throws:
  • RuntimeException – in an unlikely event of the version info
                         not being available
API Note:This method does not return null, has the return type of Optional<Runtime.Version>, or throw a checked exception. Those would warp the API to cater for something that is probably a result of a build error anyway. Hence, RuntimeException.
Returns:the version
/**
     * Returns the version of the {@code javadoc} tool and the Standard doclet.
     *
     * <p> This is typically the same as the version of the JDK platform being
     * used to run the tool, but may be different when running the tool on an
     * older version of the platform.
     *
     * @throws RuntimeException in an unlikely event of the version info
     *                          not being available
     *
     * @apiNote This method does not return {@code null}, has the return type of
     * {@code Optional<Runtime.Version>}, or throw a checked exception. Those
     * would warp the API to cater for something that is probably a result of
     * a build error anyway. Hence, {@code RuntimeException}.
     *
     * @return the version
     */
    public static Runtime.Version javadocVersion() throws RuntimeException {
        /*
         * The "jdk.javadoc.internal.tool.resources.version" resource bundle is
         * non-localized and represented by a class compiled from a source like this:
         *
         * $ cat build/.../support/gensrc/jdk.javadoc/jdk/javadoc/internal/tool/resources/version.java
         * package jdk.javadoc.internal.tool.resources;
         *
         * public final class version extends java.util.ListResourceBundle {
         *     protected final Object[][] getContents() {
         *         return new Object[][] {
         *             { "full", "15-internal+0-2020-06-02-1426246.duke..." },
         *             { "jdk", "15" },
         *             { "release", "15-internal" },
         *         };
         *     }
         * }
         *
         * The string keyed by "full" should be parseable by Runtime.Version.parse()
         */
        ResourceBundle bundle = getBundle("jdk.javadoc.internal.tool.resources.version");
        return Runtime.Version.parse(bundle.getString("full"));
    }

    
Returns a short string representation of the provided version.

 The string contains the dotted representation of the version number,
followed by the prerelease info, if any.
For example, "15", "15.1", "15.0.1", "15-internal".

Throws:
Returns:a short string representation of the provided version
/**
     * Returns a short string representation of the provided version.
     *
     * <p> The string contains the dotted representation of the version number,
     * followed by the prerelease info, if any.
     * For example, "15", "15.1", "15.0.1", "15-internal".
     *
     * @return a short string representation of the provided version
     *
     * @throws NullPointerException if {@code v == null}
     */
    public static String shortVersionStringOf(Runtime.Version v) {
        String svstr = v.version().stream()
                .map(Object::toString)
                .collect(Collectors.joining("."));
        if (v.pre().isPresent()) {
            svstr += "-" + v.pre().get();
        }
        return svstr;
    }

    
Returns a full string representation of the provided version.

 Examples of strings returned from this method are "14+36-1461" and
"15-internal+0-2020-06-02-1426246.duke...".

Throws:
Returns:a full string representation of the provided version
/**
     * Returns a full string representation of the provided version.
     *
     * <p> Examples of strings returned from this method are "14+36-1461" and
     * "15-internal+0-2020-06-02-1426246.duke...".
     *
     * @return a full string representation of the provided version
     *
     * @throws NullPointerException if {@code v == null}
     */
    public static String fullVersionStringOf(Runtime.Version v) {
        return v.toString();
    }
}